Add cancel job button and improve jobs table UI

- Remove "All Jobs" title
- Move Status column to front of table
- Add Cancel button for in-progress jobs
- Add cancel endpoint: POST /pypi/cache/cancel/{package_name}
- Add btn-danger CSS styling

backend/app/pypi_cache_worker.py

@@ -699,3 +699,37 @@ def retry_all_failed_tasks(db: Session) -> int:
 
     logger.info(f"Reset {count} failed tasks for retry")
     return count
+
+
+def cancel_cache_task(db: Session, package_name: str) -> Optional[PyPICacheTask]:
+    """
+    Cancel an in-progress or pending cache task.
+
+    Args:
+        db: Database session.
+        package_name: The package name to cancel.
+
+    Returns:
+        The cancelled task, or None if not found.
+    """
+    normalized = re.sub(r"[-_.]+", "-", package_name).lower()
+
+    task = (
+        db.query(PyPICacheTask)
+        .filter(
+            PyPICacheTask.package_name == normalized,
+            PyPICacheTask.status.in_(["pending", "in_progress"]),
+        )
+        .first()
+    )
+
+    if not task:
+        return None
+
+    task.status = "failed"
+    task.completed_at = datetime.utcnow()
+    task.error_message = "Cancelled by admin"
+    db.commit()
+
+    logger.info(f"Cancelled cache task: {normalized}")
+    return task